The two forms of liquid precipitation, drizzle and rain,
are classified in a number of ways depending on the size of the drops, the visibility
associated with the precipitation and the rate at which it falls.

Drizzle, which is defined as drops with diameters less
than 0.02 inches falling close together, usually falls from stratus clouds.
The relatively thin stratus clouds have slow, upward moving air currents. In
these conditions, cloud droplets have little time to grow before they become
too heavy for the air currents to support. The drops fall to the ground, appearing
to float in air currents. As seen in the graphic above, the intensity of drizzle
is based on the visibility at the time the precipitation is falling.

Rain, which is composed of widely separated drops with
diameters usually greater than 0.02 inches, generally falls from towering cumulus
clouds. The cumulus clouds, with fast, upward moving air currents, allow cloud
droplets to combine and grow. Raindrops can reach sizes up to 0.25 inches before
falling to the ground. The intensity of rain is based on the amount that falls
in one hour. The intensity can also be estimated visually. For more information
on the criteria for estimating rainfall intensity, refer to the Federal
Meteorological Handbook.